1. Field of the Invention
The invention relates to catheter introducers or sheaths which are inserted through the skin into a blood vessel or other body cavity to enable easy insertion, placement and withdrawal of a catheter without perforation or excess trauma to the blood vessel or cavity wall.
2. Description of the Prior Art
Prior art introducers for blood vessels generally include a thin wall tube, commonly known as a sheath, which has its distal end inserted through the skin into the blood vessel. A hub or valve housing is attached to the proximal end of the tube and contains a valve and seal structure through which a catheter is inserted into the tube and then into the blood vessel. The catheter is advanced, by using longitudinal and rotative motion, in a sometimes tortuous path through various blood vessels to place the catheter tip in the desired position. The thin wall tube, which extends for a short distance in the lumen of the blood vessel, protects the blood vessel adjacent the entrance site against perforation and abrasion from the catheter during its insertion and placement, and together with the valve and seal structure, maintains a fluid-tight relationship with the blood vessel to prevent leakage.
To insert the introducer into the blood vessel, a Seldinger type needle is often used to pierce a path through the skin and underlying tissue into the blood vessel. A guide wire is inserted through the needle and into the blood vessel after which the needle is withdrawn over the guide wire. Then an assembly of the introducer with a tubular dilator extending through the lumen of the introducer is slipped over the guide wire with the tips of the dilator and introducer being forced into the blood vessel. The dilator and guide wire are removed leaving the introducer in position to receive and guide the catheter into the blood vessel. The introducer may also include a side port downstream from the valve and seal in the housing for allowing withdrawal or infusion of fluids, such as heparin, through the introducer while the catheter is in place.
Introducer tubes must have sufficient strength, rigidity, and lubricity to enable insertion of the introducer tube into the blood vessel and to provide a low resistance pathway for a catheter being threaded into the blood vessel. Generally these requirements for strength, rigidity, and lubricity could only be met with tubes formed from polytetrafluoroethylene or high density polyethylene.
Due to the relative stiffness of the sheath, and the edge sharpness resulting from the thin wall, there is a tendency for the sheath to abrade or perforate the vessel wall either during insertion or patient movement. Also introducer tube tips have been known to split or fracture during the insertion process as a result of forces created upon being forced into body tissue.
Another problem associated with prior art introducers is the tendency for the thin walled tube to buckle or fold during insertion. The rigidity of the tube sometimes causes the wire guide to bend or fold or the tip to snag on tissue to thus lead to a buildup of forces in the tube to cause the buckling or folding of the tube commonly near to the junction of the housing with the tube. These folds have been known to impede catheter introduction or to restrict fluid delivery. Also these folds can promote thrombus formation due to blood retention at the fold site.
U.S. Pat. No 4,610,674 discloses a catheter introducer having a reinforcing coil body fitted in a connecting portion of the hub and extending axially of the sheath from the connection portion toward the distal end of the sheath beyond the connection portion. The reinforcing coil prevents folding of the sheath at the junction of the sheath and hub.
Soft tips are commonly employed on catheters in order to avoid injury to blood vessels. For example, U.S. Pat. No. 4,563,181 discloses a tubular body portion of a catheter formed from nylon-11 with a soft tubular tip formed from a blend of nylon-11 and an ester linked polyether-polyamide copolymer commonly known as polyether block amide (PEBA) fused onto the distal end of the tubular body portion. The tips of catheters are made soft so that they avoid penetration through blood vessel walls.
The use of a coating of hydrogel material including polyvinylpyrrolidone-polyurethane interpolymer on catheters to reduce insertion friction and to reduce thrombogenicity is disclosed in U.S. Pat. No. 4,100,309 to Micklus et al. The disclosed hydrogel material has been successfully coated on polyurethane catheters and silicone wound drains. It has been disclosed that the hydrogel material will also adhere to polyvinyl chloride, polymethyl methacrylate, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polytetramethylene terephthalate, latex rubber and polyisoprene. The hydrogel material can be applied to fluorocarbons and polyolefins which have been subjected to surface preparation to assure adequate wetting and bonding of the coating. The coating, when exposed to water, swells and develops a low coefficient of friction.